With regard to a network in a data center, to cope with an increase in communications between servers, the network may be structured in a manner that a plurality of routes that can be simultaneously used exist between the servers in some cases. For example, a certain literature discloses a technology for a multipath communication by a communication apparatus that can be coupled to a plurality of networks.
In addition, in order that a cloud service can be provided without delay, an overlay network based on a VXLAN (Virtual eXtensible Local Area Network) technology is structured, and a virtual network may be structured by tunnel coupling of servers of respective tenants in some cases. In the overlay network based on the VXLAN technology, a transfer route of a packet varies based on information set in an external header of an encapsulated packet.
A certain literature discloses a technology for checking statuses of respective routes in the overlay network based on the VXLAN technology. Specifically, a plurality of packets are transmitted with respect to a list of specified target hosts while source port numbers in the external headers of the packets are changed, and reachability of the packet is determined based on a response to the transmission.
A value set in the external header is calculated by a hash calculation of information included in an internal header, but an algorithm of the hash calculation and an algorithm of a transfer by a switch depend on an implementation, which is not necessarily revealed in advance. For this reason, in a case where a communication abnormality occurs, it is not possible to identify the transfer routes of the packets depending on the above-mentioned technology, and it is not possible to control the transfer routes of the packets. In addition, the number of probe packets transmitted to check the statuses of the respective routes is increased in a case where the above-mentioned technology is used, which affects the transfer of the normal packet other than the probe packet. Related-art technology literatures include Japanese Laid-open Patent Publication No. 2009-296084, Aijay Adams and two others, “NetNORAD: Troubleshooting networks via end-to-end probing”, Changhoon Kim, Parag Bhide, Ed Doe, Hugh Holbrook, Anoop Ghanwani, Dan Daly, Mukesh Hira, Bruce Davie, “In-band Network Telemetry (INT)”, and Petr Lapukhov, “Move Fast, Unbreak Things! Network debugging at scale”.